A machine tool includes at least one linear axis and/or rotational feed axis (below, these linear axis and rotational feed axis sometimes being simply called “feed axes”). The motors for driving these feed axes are controlled by a numerical control device. In a machine tool, different tools are attached in accordance with the content of machining of the workpiece. Further, jigs for attaching the workpieces to the machine tool are also designed for the specific workpieces.
In such a machine tool, the work table on which the workpiece is set or the tool is made to move in two mutually perpendicular directions whereby the workpiece is for example made to move along an arc-shaped path. In the case of such machining, sometimes the servo motor for one feed axis is operated while the servo motor for the other feed axis is stopped for an instant and then restarted.
Therefore, the output shaft of the other servo motor changes from a dynamic friction state to a static friction state and then again to a dynamic friction state. Furthermore, at the time of reversal of a servo motor, the effects of backlash and elastic deformation are felt in the transmission system of the servo motor. For this reason, a delay in response occurs in the operation of the other servo motor. This appears in measured values as a stick motion P. For this reason, when cutting a workpiece for example along an arc, the problem arises of the workpiece being excessively cut at the cutting location corresponding to the stick motion P.
To solve this problem, in PLT 1, a correction command is added to a position command to thereby suppress stick motion.